An extended-family study of caries susceptibility among the demes of a descrete, isolated population is proposed. The effects of diet, natural fluoridation and oral hygiene will be rigorously assessed, and the range of population variation in carious lesions will be determined between and within pedigrees. Genetic and environmental contributions to the variance will be estimated by path analysis and major gene affects will be investigated by pedigree analysis. Thus the probable mode of inheritance as well as the magnitude of any host factors will be specificable. The proposed research constitutes a unique opportunity to bring strict genetic control to the study of caries prevalence cross-sectionally.